The invention relates to a method for the manufacture of brushware, particularly brushes.
In the manufacture of brushware, particularly brushes, paint brushes, mats, pads, floor coverings, etc., it is necessary to connect in one piece to a bristle carrier a plurality of single bristles or bristle bundles. The prior art discloses various methods for this purpose, but all suffer from certain disadvantages.
Since the first use of plastics both for bristles and for the bristle carrier, numerous attempts have been made to replace the earlier mechanical fastening of the bristles or bristle bundles to the bristle carrier by a positive or integral connection without any other mechanical fastening means. An important quality feature for brushware is the extraction or pull-out resistance of the individual bristles or bristle bundles, i.e. the bristles must be embedded in the plastic mass of the bristle carrier in such a way that they are not released or detached under the forces occurring during use. Of the known methods, only those have proved to be usable in which a thickened portion is provided on the bundle ends and which following the introduction into the plastic mass of the bristle carrier forms a type of anchor and also interconnects the bristles at their fastening-side end, so that the extraction forces acting on the bundle or also only on the individual bristles is introduced into the thickened portion and absorbed by the fixture thereof in the bristle carrier.
It is known from DE 36 37 750 A1 to form in the bristle carrier blind holes and to heat the plastics material surrounding the blind holes until it becomes flowable. Subsequently a unwelded or welded bristle bundle with the anchoring end is pressed into the melted blind hole, so that the bristles are held in the bristle carrier. However, it is frequently additionally necessary to have a mechanical sealing or compression of the melt in the vicinity of the hole rim. However, the particular disadvantage of this method is that the necessary heating of the bristle carrier material must take place into the thermoplastic range with very precisely chosen, relatively low heating temperatures. As a result of the slow heating, this method leads to relatively long cycle times, which is uneconomic. In the case of one-sided heating of the bristle carrier, there is a danger of the latter distorting. It is also very difficult to introduce in planned manner thermal energy into a plurality of closely adjacent blind holes, because especially with very small brushes there is a risk of the blind holes collapsing on heating. On feeding individual bristles into the blind holes, the problem arises that the low flexural strength of the single bristles is further significantly reduced when they are heated, so that during feeding there can be a lateral moving aside of the bristles.
It is also known to weld the bristles to the bristle carrier. For this purpose the bristles or bristle bundles and the bristle carrier, which are made from the same material, are heated to a thermoplastic state and then the two components are pressed onto one another. Due to the strong heating of the bristles, there is a molecular reorientation of the bristle material and consequently a marked deterioration of the flexural strength of the individual bristles, together with a reduction of their tensile strength. In a variant of the method, at the end of the bristles or bristle bundle can be formed slightly thickened heads. As the two components are only connected via the materials flowing together at the connection points, there is not always an adequate connection between the two components. In addition, this method also leads to relatively long cycle times. During the welding of the bristles or bristle bundles, weld feet form on the bristle carrier, so that the latter has a stepped surface, in which can collect bacteria or other impurities. This makes it much more difficult to clean the brush and is also extremely unhygienic.
It is particularly difficult to fasten single bristles with an adequate quality in the blind holes of a bristle carrier. When heating an individual or single bristle a drop forms, which exceeds the diameter of the very small blind hole, into which the single bristle is to be introduced. On inserting the single bristle, there is consequently a smearing of the plastics material, so that a reliable connection between the single bristle and the bristle carrier is not ensured. In the case of a supply of the single bristle in the heated state into the blind hole, a buckling can occur if the single bristle is compressed, so that it is not possible to achieve a correct, mutual orientation of a plurality of single bristles.
It is desirable both for the bristles, which are generally of higher grade plastics, such as polyamides, and the bristle carrier, to keep the material use as low as possible, which would be implementable by a correspondingly short fixture of the bristles. Brushware also exists, in which the bristle carrier is to have a minimum wall thickness for use reasons. This e.g. applies with toothbrushes, so that due to the constricted conditions in the oral cavity, a shallow or flat construction, including the bristle length is ensured.
The know methods also suffer from the disadvantage that the flexural strength or bending elasticity (re-righting capacity) of the bristles resulting from the stretching and thermal stabilization of the monofilaments is impaired by the melting of the bristle ends in connection with the formation of the thickened portion. In the heated area of the bristles there is a molecular reorientation and consequently a deterioration of the bending behaviour of the single bristle and a reduction of tensile strength. This can only be counteracted by an adequately large embedding length and consequently a lateral support of the bristle, but this is disadvantageous for the reasons indicated hereinbefore.
The problem of the invention is to provide a method for the manufacture of brushware, particularly brushes, in which in the case of a low material use, an adequate extraction resistance of the individual bristles and also the bundles is achieved, the bending elasticity and re-righting capacity of the bristles are maintained and which ensures a high productivity during the manufacture of the brushware.